A customer called in and explained that he needs to permanently blacklist a MAC address. He has followed the 6.4.x User Guide, and set the blacklist-time to "0" (indefinite), but the GUI and the CLI still show the blackout timer is counting down from 3600 seconds (default) for that MAC address.

From the 6.4.x User Guide, page 558 (Blacklisting Manually)

stm add-blacklist-client <macaddr>

From the 6.4.x User Guide, page 560 (Setting Blacklist Duration)

For clients that are blacklisted due to other reasons, including manual blacklisting. By default, this is set to
3600 seconds (one hour). You can set this to 0 to blacklist clients indefinitely.